Possible Clues:

• Element that can exist as a purple vapour
• What I might be in a lab?
• Halogen element utilised by the thyroid gland
• Chemical element whose atomic number is 53-Across
• First aid tincture
• Halogen element
• Antiseptic or dye
• Have a meal after ten -- it's good for health
• Chemist's "I"
• Element essential to thyroid function